Conventionally, as a fastening method, there has been a fastening method using a bolt and a nut. The fastening method using the bolt and the nut is structured such that an axial force (an elastic energy) stored in a shaft of the bolt acts as a force for pulling in an axial direction of the bolt on thread surfaces of the bolt and the nut, thereby preventing the bolt and the nut from being loosened on the basis of a friction force generated on the thread faces so as to fasten a fastened member. Accordingly, it is necessary to securely store the axial force in the shaft of the bolt, however, about 90% of a fastening torque is lost due to a friction between a seat surface of the nut and the fastened member and a friction of the thread surface at a time of screwing and fastening the nut to the bolt, and only about 10% of the fastening torque can store the axial force in the shaft of the bolt. As mentioned above, since it is impossible to sufficiently store the axial force in the shaft of the bolt, there has been a problem that the bolt and the nut are loosened due to a repeated load and a vibration applied to the fastened member.
Further, there are risks that the friction force between the seat surface of the nut and the fastened member and the friction force of the threaded portions are scattered, and the seat surface of the nut and the fastened member, and the threaded portions are gnawed or seized, whereby the axial force stored in the shaft of the bolt is not stable, and the bolt and the nut are loosened. Accordingly, in the case of fastening a high strength portion, there is employed a countermeasure of applying a friction coefficient stabilizing agent to a thread ridge of the bolt, thereby stabilizing the axial force of the bolt. Therefore, there is a problem that a cost is increased.
Accordingly, in the case that a detachment of the fastening is not allowed, there is used a non-disassemble swage method, as shown in U.S. Pat. No. 4,347,728. The non-dissemble swage method is a method of inserting a pin 51 having a parallel groove 51a formed on a surface of a shaft to a fastened member 52, thereafter setting a collar 53 from a leading end 51b of the pin, caulking the collar 53 from both sides while pulling the leading end 51b of the pin by a special tool (not shown) and fastening the fastened member, as shown in FIG. 18. In accordance with this method, it is possible to securely apply the axial force to the pin 51. However, in accordance with this non-assemble swage fastening method, since it is necessary to break the pin 51 and the collar 53 by the special tool at a time of detaching, there is a problem that the pin 51 and the collar 53 can not be reused, as well as a detaching work becomes complicated.
Accordingly, there has been proposed a swage fastening method as shown in Japanese Patent No. 2672190. The swage fastening method is a method of inserting a Hacks pin 61 (trade mark) in which a spiral lock groove 61a is formed as shown in FIG. 19 in place of the parallel groove 51a to a fastened member 62, setting a collar 63 from a leading end 61b of the pin, and caulking the collar 63 from both sides while pulling the leading end 61b of the pin by a special tool (not shown) so as to fasten the fastened member.
In the swage fastening method using the Hacks pin 61 (trade mark), it is possible to detach the collar 63 from the Hacks pin 61 (trade mark) by gripping the collar 63 so as to rotate without breaking the Hacks pin (trade mark) and the collar 63 at a time of detaching. However, since the collar 63 is caulked so as to be fastened, there has been a problem that the once detached collar 63 can not be reused.
Further, in the fastening methods mentioned above, since the collars 53 and 63 are plastically deformed so as to be caulked, it is assumed to use a soft material. In order to correspond to a high axial force, there has been a problem that it is necessary to set a height of the collars 53 and 63 high. Further, in the axial force fastening method, since the collars 53 and 63 are caulked, a surface treated layer such as a plating or the like applied to the surfaces of the collars 53 and 63 is scratched, and there has been a problem that a rust proofing countermeasure is necessary.